Some brewers (not many anymore) use isinglass, finings or other animal products in the production of their beverages. Vegan vanguard is always my first choice because she's non-judgy:
Also, I believe in supporting your local brewers. I asked Rick at Triangle Brewing Company if his beers contained isinglass and he replied "Heck no! We make vegan beer!" That makes me want to buy his beer EVEN more, which helps his business and my community. Even if your local brewer does use animal products, just asking whether or not the beer is vegan will get a businessperson thinking. Before you know it, there might be a special vegan offering all because of you!